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991.
Shin-ichiro Gozu Kouichi Akahane Naokatsu Yamamoto Akio Ueta Naoki Ohtani 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):230
InGaAs/AlAsSb systems lattice matched to InP have two distinguishable features: a high conduction band offset and type-II band configuration. Although, the former results in a large intersubband transition (ISBT) at conduction band, the latter makes it difficult to use the effective interband transition (IBT). To overcome this latter problem, the effect of the Sb was investigated because Sb would act as a band modulator from type-II to type-I. In0.57Ga0.43As1-xSbx/AlAs0.48Sb0.52 single quantum well (SQW) samples with various Sb compositions x, were grown on GaAs substrates via AlAs0.48Sb0.52 buffer layer. Their photoluminescence (PL) properties were examined to identify their band configurations. When the excitation laser power was increased, the PL property of In0.57Ga0.43As SQW sample, showed a larger blue shift than that of ones. This indicates that the band configuration modulates from type-II to type-I when the antimonide composition is larger than 0.13. These findings indicate that new functional devices can be fabricated using a combination of IBT and ISBT. 相似文献
992.
Recent evidence for involvement of internal water molecules in the mechanism of bacteriorhodopsin is reviewed. Water O-H stretching vibration bands in the Fourier transform IR difference spectra of the L, M and N intermediates of bacteriorhodopsin were analyzed by photoreactions at cryogenic temperatures. A broad vibrational band in L was shown to be due to formation of a structure of water molecules connecting the Schiff base to the Thr46-Asp96 region. This structure disappears in the M intermediate, suggesting that it is involved in transient stabilization of the L intermediate prior to proton transfer from the Schiff base to Asp85. The interaction of the Schiff base with a water molecule is restored in the N intermediate. We propose that water is a critical mobile component of bacteriorhodopsin, forming organized structures in the transient intermediates during the photocycle and, to a large extent, determining the chemical behavior of these transient states. 相似文献
993.
[reaction: see text] Catalytic asymmetric allylation of 3,4-dihydro-6,7-dimethoxyisoquinoline was carried out using allyltrimethoxysilane in the presence of Cu(I) and tol-BINAP. The allyl adduct thus obtained was transformed to a chiral synthetic intermediate for (-)-emetine in good yield. The procedure was applied to the total synthesis of ent-emetine. 相似文献
994.
[reaction: see text]. A method was found for the novel synthesis of ortho ester derivatives that are potentially useful as selective epsilon opioid receptor ligands. An unexpected 17-(cyclopropylmethyl)-4,5alpha-epoxy-6alpha-hydroxy-3,7,7-trimethoxy-8-oxa-6,14-endoethanomorphinan was produced when 17-(cyclopropylmethyl)-4,5alpha-epoxy-3-methoxy-6alpha,14-dihydroxy-6beta-(1,3-dithia-2-yl)-morphinan was treated in methanol with trimethyl orthoformate and CuO/CuCl2. This ortho ester derivative was then converted to an ester with acid. The structure of the ortho ester was determined by 2D NMR (HMBC) and mass spectra. 相似文献
995.
Umemura T Ueki Y Tsunoda K Katakai A Tamada M Haraguchi H 《Analytical and bioanalytical chemistry》2006,386(3):566-571
Hexyl methacrylate (HMA)-based monolithic semi-micro columns were prepared by in situ polymerization within the confines of
1.02-mm-i.d. silicosteel tubing for reversed-phase and/or precipitation–redissolution liquid chromatography. Practically useful
monolithic columns with adequate separation efficiency, high permeability, and good mechanical strength were successfully
obtained using a polymerization mixture comprising 24% hexyl methacrylate (HMA), 6% ethylene dimethacrylate (EDMA), 44.5%
1-propanol, and 25.5% 1,4-butanediol. The column performance was evaluated through the separations of a series of alkylbenzenes.
At a normal flow rate of 50 μL min−1, the produced HMA-based monolithic columns typically exhibited 3,000 theoretical plates for a 20-cm-long column, and the
pressure drop was generally less than 1 MPa per 20 cm. The monolithic columns were resistant to at least 15 MPa, and could
be properly operated at 15–20 times higher flow rate than normal, reducing the separation time to 1/15–1/20. The HMA-based
monolithic columns were applied to rapid and efficient separations of proteins such as ribonuclease A, cytochrome c, transferrin,
and ovalbumin in the precipitation–redissolution mode. Using a CH3CN gradient elution at a flow rate of 1,000 μL min−1, four proteins were baseline separated within 20 s. 相似文献
996.
(E,E)-1,4-Diphenylbutadiene derivatives were synthesized by utilizing the Stobbe reaction of dimethyl succinate as a key step. Their stereoisomers were also synthesized stereoselectively by means of the cross-coupling reaction of the vinylstannanes and the vinylbromides, which were obtained from the propiolic acid esters by stereoselective hydrostannation, as a key step. To discover novel stimulators of fibrinolysis in vascular endothelial cells, the synthesized compounds were added to cultured bovine endothelial cells to determine the activity of the plasminogen activator in the conditioned medium. Of the synthesized compounds, three compounds were found to stimulate the activity of the plasminogen activator in endothelial cells. In addtition, these compounds inhibited thrombus formation in a rat model of venous thrombosis. 相似文献
997.
Shibusawa Y Yamakawa Y Noji R Yanagida A Shindo H Ito Y 《Journal of chromatography. A》2006,1133(1-2):119-125
Three-phase solvent systems were efficiently utilized for high-speed counter-current chromatography (HSCCC) to separate multiple components with a wide range of hydrophobicity. The compositions of three-phase systems were optimized according to their physical parameters such as volume ratio, viscosity and specific gravity of upper (UP), middle (MP) and lower (LP) phases. The three-phase systems composed of n-hexane-methyl acetate-acetonitrile-water (4:4:3:4, v/v/v/v) was selected for HSCCC separation of a mixture of 15 standard compounds with a wide range in hydrophobicity from beta-carotene to tryptophan. The separation was initiated by filling the column with a mixture of MP and LP both as a stationary phase followed by elution with UP to separate the hydrophobic compounds. Then the mobile phase was switched to MP to elute the moderately hydrophobic compounds, and finally the polar compounds still retained in the column were fractionated by eluting the column with LP. The system successfully resolved all 15 compounds in one-step operation in 70 min. 相似文献
998.
To investigate the resolution of secondary alcohols using 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid), 2-methyl-4-heptanol, one of the aggregation pheromones of Metamasius hemipterus, was resolved using (S)-MalphaNP acid. As a chiral-resolving agent, MalphaNP acid is superior to 3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid (MTPA) in terms of HPLC separation and NMR shielding. A better separation of diastereomeric MalphaNP esters was observed when n-hexane-THF was used as the eluent for silica gel HPLC. The solvolysis of the diastereomeric MalphaNP esters gave (R)-2-methyl-4-heptanol and its enantiomer; enantiopure (S)-MalphaNP acid was also recovered. In addition, the preferred conformation of the MalphaNP ester was confirmed using methyl (R)-3-hydroxyvalerate as an authentic compound. 相似文献
999.
Honda K Nakata E Ojida A Hamachi I 《Chemical communications (Cambridge, England)》2006,(38):4024-4026
We have successfully developed a ratiometric detection system for protein of interest using the complementary recognition pair of the tetra-aspartate peptide tag and the SNARF-appended Zn(ii)-DpaTyr probe. 相似文献
1000.
Akio Saito 《Tetrahedron letters》2010,51(11):1471-4661
In the presence of Pd2(dba)3-Cy3P catalyst, IPr·HCl salt [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], and Cs2CO3, N-propargylamides react with allyl carbonates to give 2,5-disubstituted oxazoles having homoallyl groups through the tandem cycloisomerization-allylation. 相似文献